1. Field of the Invention
The present invention relates to photosensitive polymers used in chemically amplified photoresist compositions, and photoresist compositions including such polymers.
2. Description of the Related Art
With increasing integration of semiconductor devices, there is a heightened need in photolithography for photoresists that form a fine pattern line of less than 0.25 .mu.m. Photolithography technology has now been developed that can be used with an ArF excimer laser (e.g., .lambda.=193 nm) to fabricate semiconductor devices having more than a 1 gigabit capacity. This technology is intended to replace the conventional KrF excimer lasers which expose photoresist films using deep ultraviolet rays (.lambda.=248 nm). It is therefore desirable to develop new chemically amplified photoresist compositions that produce a fine pattern line of less than 0.25 .mu.m when exposed using an ArF excimer laser.
Chemically amplified photoresist compositions for use with an ArF excimer laser should possess the following qualities:
(1) excellent transmittance in the range of 193 nm; PA1 (2) excellent thermal characteristics, such as for example, a high glass transition temperature (Tg), and a thermal decomposition temperature (Td) higher than its Tg so that the photoresist can be baked to a temperature that is above the (Tg) before being exposed in order to vaporize unwanted organic solvents and to make the photoresist film hard, without causing the photoresist to decompose; PA1 (3) excellent adhesion to film materials; PA1 (4) excellent resistance to dry etching; and PA1 (5) the capability of being developed using conventional alkaline developers, such as 2.38 weight percent (wt %) tetramethylammonium hydroxide(TMAH).
One example of a polymer that has been reported to possess the above properties is the photosensitive terpolymer poly(MMA-tBMA-MAA) which is represented by the following chemical formula: ##STR1##
However, poly(MMA-tBMA-MAA) is not an ideal polymer for making photoresist compositions because it has a very weak resistance to dry etching, it has weak adhesive properties, and a special developer is needed. Methacrylate polymers are generally used in the photoresist resist materials for photolithography processes that use an ArF excimer laser. However, such polymers have a very weak resistance to dry etching. To increase resistance to dry etching, a polymer having a backbone composed of an alicyclic compound such as an isobornyl group, an adamantyl group, or a tricyclodecanyl group is used. These conventional polymers, however still exhibit weak resistance to dry etching. They also have inadequate adhesion characteristics, which means that a resist layer formed using the polymer may lift from the underlying layer, thus forming a photoresist pattern that is not sharp enough. These polymers also require special developers.